ios: Default GYP_GENERATORS to ninja, and error out if GYP_GENERATORS is xcode

build/gyp_environment.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Sets up various automatic gyp environment variables. These are used by
 gyp_chromium and landmines.py which run at different stages of runhooks. To
 make sure settings are consistent between them, all setup should happen here.
 """
 
 import gyp_helper
 import mac_toolchain
 import os
 import sys
 import vs_toolchain
 
 def SetEnvironment():
   """Sets defaults for GYP_* variables."""
   gyp_helper.apply_chromium_gyp_env()
 
   # Default to ninja on linux and windows, but only if no generator has
   # explicitly been set.
   # Also default to ninja on mac, but only when not building chrome/ios.
   # . -f / --format has precedence over the env var, no need to check for it
   # . set the env var only if it hasn't been set yet
   # . chromium.gyp_env has been applied to os.environ at this point already
-  if sys.platform.startswith(('linux', 'win', 'freebsd')) and \
+  if sys.platform.startswith(('linux', 'win', 'freebsd', 'darwin')) and \
       not os.environ.get('GYP_GENERATORS'):
     os.environ['GYP_GENERATORS'] = 'ninja'
-  elif sys.platform == 'darwin' and not os.environ.get('GYP_GENERATORS') and \
-      not 'OS=ios' in os.environ.get('GYP_DEFINES', []):
-    os.environ['GYP_GENERATORS'] = 'ninja'
 
   vs_toolchain.SetEnvironmentAndGetRuntimeDllDirs()
   mac_toolchain.SetToolchainEnvironment()